A light emitting diode (LED) is a semiconductor diode for radiating light, and has a function of converting an electrical energy into ultraviolet light or visible light.
Conventionally, there has been widely utilized a light emitting device using an LED lamp. The LED lamp is manufactured, for example, in such a manner that a light emitting chip is formed by using a substrate such as a transparent substrate or the like and a light emitting material such as GaP, GaAsP, GaAlAs, GaN, InGaN, AlGaN, InGaAlP or the like, then the light emitting chip is sealed by a transparent resin.
When various phosphors are contained in a sealing resin, the LED lamp is able to adjust a color of the emitting light. That is, when a light emitting chip for emitting a light and a phosphor powder for absorbing the light and releasing a light having a predetermined range of wavelength are combinatory used, it becomes possible to emit a light or a white light having a visible wavelength range, by the actions of the light emitted from the light emitting chip and the light emitted from the phosphor powder.
As the white light emitting LED lamp for emitting the white light, a white light emitting LED lamp using a blue light emitting diode chip and a white light emitting LED lamp using a UV light or a violet light emitting diode chip are well known.
As the white light emitting LED lamp using a blue light emitting diode chip, there have been well known: an LED lamp in which a blue light emitting diode chip and a red light emitting phosphor (red phosphor) and a green light emitting phosphor (green phosphor) or the like are combined, (hereinafter referred to as “white LED lamp type 1”); and an LED lamp using a blue light emitting diode chip and an yellow light emitting phosphor (yellow phosphor) such as YAG or the like are combined, (hereinafter referred to as “white LED lamp type 2”).
Furthermore, as the white light emitting LED lamp using a UV light or violet light emitting diode chip, there has been well known an LED lamp in which a UV light or violet light emitting diode chip and a red phosphor, a green phosphor and a blue phosphor or the like are combined, (hereinafter referred to as “white LED lamp type 3).
Because a color of the light emitted from the white LED lamp is white, the white LED lamp is used as a light source for a backlight of a liquid crystal display device and a light source of an illumination device or the like.
The white LED lamp used as the light source for the backlight of the liquid crystal display device is demanded to have various color qualities such that a color reproducing property is wide, the lamp can be designed to comprise a predetermined white chromaticity, a scattering of the chromaticity is small, and the like.
Further, the white LED lamp used as the light source for the illumination device is demanded to have various color qualities such that a color rendering property is excellent, the lamp can be designed to comprise a predetermined white chromaticity, a color unevenness is small, a scattering of the chromaticity is small, and the like.
Therefore, in a case where the white LED lamp is used as the light source for the backlight of the liquid crystal display device, the white LED lamps of type 1 and type 2 have raised the following problems.
Namely, the white LED lamp of type 1 has drawbacks such that the color unevenness is large, the scattering of the chromaticity is also large, and the like. On the other hand, the white LED lamp of type 2 have drawbacks such that the color reproducing property is narrow, the color rendering property is not good, and the lamp can not be designed to comprise a predetermined white chromaticity, and the like.
In contrast, according to the white LED lamp of type 3, it is possible to satisfy the various color qualities such that the color reproducing property is broad, the lamp can be designed to comprise a predetermined white chromaticity, the color rendering property is good, and the color unevenness is small, and the like. Therefore, the white LED lamp of type 3 is suitable as the light source for the backlight of the liquid crystal display device and the light source of the illumination device.
For example, Japanese Patent Application (Unexamined Publication) No. 2005-191420 (patent Document 1) discloses a white LED lamp of type 3. According to this white LED lamp, a luminous efficiency is increased to be high.
On the other hand, in recent years, conventional Brown-tube televisions as various display device have been replaced with thin-model television represented by a liquid crystal television or a plasma television. The above display device is disclosed in Japanese Patent Application (unexamined publication) No. 2000-49380 and Japanese Patent Application (unexamined publication) No. HEI 10-187062 (refer to Patent Documents 2 and 3). The advantages and the disadvantages of the above display devices are collectively shown in Table 3.
As is clear from the results shown in Table 3, the advantages and the disadvantages of the display devices vary in the respective technical points. However, a main reason, why demand and market are shifting from Brown-tube televisions to the thin-model televisions such as liquid crystal television, plasma television or the like, has been confirmed that the problem is a large depth, weight and size of the television rather than a problem of displayed image per se of the television. Accordingly, if the problem of the large size is solved while a favorable characteristic of Brown tube television is maintained as it is, it is said that an ideal display (display device) can be actually realized.    Patent Document 1: Japanese Patent Application (Laid-Open) No. 2005-191420.    Patent Document 2: Japanese Patent Application (Laid-Open) No. 2000-49380.    Patent Document 3: Japanese Patent Application (Laid-Open) No. HEI 10-187062